Gas assisted method for applying resist stripper and gas-resist stripper combinations

ABSTRACT

A method for moving resist stripper across the surface of a semiconductor substrate. The method includes applying a wet chemical resist stripper, such as an organic or oxidizing wet chemical resist stripper, to at least a portion of a photomask positioned over the semiconductor substrate. A carrier fluid, such as a gas, is then directed toward the semiconductor substrate so as to move the resist stripper across the substrate. The carrier fluid may be directed toward the substrate as the resist stripper is being applied thereto or following application of the resist stripper. A system for effecting the method is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/165,261,filed Jun. 6, 2002, now U.S. Pat. No. 6,576,561, issues Jun. 10, 2003,which is a divisional of application Ser. No. 09/639,550, filed Aug. 16,2000, now U.S. Pat. No. 6,440,871, issued Aug. 27, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods for strippingphotoresist from a semiconductor device structure and, in particular, tomethods for continuously moving resist stripper across the surface of asemiconductor device structure. More particularly, the present inventionrelates to resist stripper application methods that include exposing theresist stripper to a gas, to move the resist stripper across thesemiconductor device structure, to thin the resist stripper, or tootherwise increase the rate at which the resist stripper removesphotoresist from the semiconductor device structure.

2. Background of Related Art

In fabricating semiconductor devices, several material layers, includingelectrically conductive and insulative layers, are formed and patternedto build various structures upon an active surface of a semiconductorsubstrate, such as a wafer or other large-scale substrate formed fromsemiconductive material (e.g., silicon, gallium arsenide, or indiumphosphide), thereby forming a semiconductor device structure.

The material layers formed over a semiconductor substrate are typicallypatterned by forming masks thereover. Photomasks are often employed. Theformation of photomasks involves the use of a photoresist material thattakes on a specific pattern as the photoresist material is exposed toradiation, such as one or more visible wavelengths of light, through areticle. In this manner, the reticle and the radiation transmittedtherethrough together define the specific pattern of the photoresist.The photoresist is then developed, or cured, so as to maintain thepattern and to form a photomask, which is commonly referred to in theart as a “photoresist” or simply as a “resist.” Once the photomask hasbeen formed, one or more underlying material layers may be patternedthrough the photomask, such as by way of wet or dry etching processes.

After one or more layers underlying a photomask have been patternedthrough the photomask to form a semiconductor device structure, thephotomask is typically removed. Various processes are known for removingphotomasks. Typically, a thin layer of a resist stripper is applied tothe semiconductor device structure, such as by spraying the resiststripper onto the semiconductor device structure. Alternatively, asemiconductor device structure bearing a photomask is immersed, ordipped, into a bath of wet chemical resist stripper.

One type of resist stripper that may be used to remove a photomask froma semiconductor device structure is a wet chemical resist stripper, suchas an organic resist stripper (e.g., phenol-based and phenol-freeorganic strippers) or an oxidizing resist stripper (e.g., solutions ofsulfuric acid (H₂SO₄) and an oxidant, such as hydrogen peroxide (H₂O₂)or ammonium persulfate). Wet chemical resist strippers typically remove,or dissolve, the photomask with selectivity over (i.e., at a faster ratethan) the material of the structures and material layers that underlieand that may be exposed through the photomask or upon removal of thephotomask material from the semiconductor device structure. Some suchwet chemical resist strippers include one or more types of activechemicals that remove photomasks by reacting with the material ormaterials of the photomasks. Thus, the concentrations of activechemicals in these wet chemical resist strippers decrease over time,thereby reducing the effectiveness of these resist strippers. Moreover,as the concentrations of reaction products increase in locations wherefurther stripping is desired, the rate at which further reactionsbetween the resist stripper and the photoresist may occur and, thus, therate at which the photoresist is removed from the semiconductor devicestructure, are reduced.

As another example, ozonated water may be used as a resist stripper toremove a photomask from a semiconductor substrate. Typically, the wateris heated to enhance the ability of the ozone dissolved therein toremove a resist layer from a semiconductor substrate. The heated,ozonated water may be applied to the resist-covered substrate byspraying. As those of skill in the art are aware, ozone effervesces fromwater relatively quickly. Thus, ozonated water resist strippers losetheir effectiveness over time. In addition, as with other types ofresist strippers, the rates at which ozonated water resist strippersremove photoresists may be reduced as the concentrations of reactionproducts increase in the resist stripper.

Conventional processes for applying resist strippers to resist, such asspraying or immersion, do not facilitate continuous movement of theresist strippers across the semiconductor device structure followingapplication and may, therefore, permit the resist strippers to sit, orstagnate, on the resist. Stagnation of resist strippers is somewhatundesirable, however, as the concentrations of reaction products mayincrease during stagnation and stagnation may, therefore, reduce therate at which the resist strippers remove photomasks from semiconductordevice structures. In addition, when a wet etchant is employed as theresist stripper, the active chemical reactant or reactants of the resiststripper may react with the photomask and, therefore, decrease inconcentration. As a result, in a stagnant area, the rate at which such awet etchant resist stripper removes the photomask and, thus, the abilityof such a wet etchant resist stripper to remove the photomask, decreasesover time.

In the ozonated water example of a resist stripper, when the resiststripper is at rest, ozone escapes from the water into the atmosphereover time. As the concentration of ozone in the ozonated water resiststripper decreases, the effectiveness of the resist stripper, as well asthe rate at which a photomask is removed from a semiconductor substratetherewith, are reduced.

When conventional stripping methods are employed, ozonated water resiststrippers typically remove hard-baked photoresist at a rate of about4,000 Å per second to less than about 8,000 Å per second.

The art lacks teaching of methods for introducing one or more gases intoor onto a resist stripper to maintain a desired rate for strippingresist from a semiconductor device structure, as well as strippingsystems for effecting such methods.

SUMMARY OF THE INVENTION

The present invention includes a method and system for stripping resistsfrom semiconductor substrates while maintaining a desired rate of resiststripping. The method of the present invention includes applying aquantity of resist stripper onto a semiconductor device structure anddirecting at least one carrier fluid, such as a gas other than ozone,toward the resist stripper or forming at least one gas other than ozonein the resist stripper.

The resist stripper is applied to the semiconductor device structure ina manner that the resist stripper contacts at least a portion of aphotomask, or resist, to be removed. For example, the resist strippermay be hot ozonated water that includes a concentration sufficient toremove the resist at a desired rate. Other types of resist strippers,such as wet chemical resist strippers, may also be used in accordancewith teachings of the present invention. The resist stripper may beapplied to at least a portion of the semiconductor device structure byspraying, in a stream, by dipping the semiconductor device structure inthe resist stripper, or otherwise, as known in the art.

The resist stripper may be exposed to one or more gases or other carrierfluids prior to, during, or after application thereof onto a photoresiston the semiconductor device structure. The one or more other, non-ozonegases may thin the layer of resist stripper over the semiconductordevice structure or move the resist stripper across a surface of thesemiconductor device structure, both of which prevent the formation ofor eliminate macroscopic drops of resist stripper on the semiconductordevice structure. Alternatively, the one or more gases may be theproduct of one or more chemical reactions effected by or in the resiststripper, in which case the one or more gases are formed in the resiststripper. In any event, by exposing the resist stripper to one or moregases or other carrier fluids, the rate at which the resist stripperremoves photoresist from the semiconductor device structure isincreased.

As an example of the manner in which resist stripper may be moved acrossthe surface of the semiconductor device structure, one or more gasesunder pressure, such as in a jet or stream of liquid or gas, may bedirected at least partially across the surface of the semiconductordevice structure so as to force resist stripper across the semiconductordevice structure. This movement of resist stripper across the surface ofthe substrate prevents stagnation of the resist stripper and,consequently, prevents a reduction in the rate at which the resiststripper removes the photomask from the semiconductor substrate.

The one or more gases may be directed across the surface of thesemiconductor device structure substantially simultaneously with theresist stripper, either by combining the gas or gases with the resiststripper or separately from the resist stripper. Alternatively, the gasor gases may be directed across the semiconductor device structure afterthe resist stripper has been applied to the semiconductor devicestructure. When the one or more gases are directed across the surface ofthe semiconductor device structure, the one or more gases force theresist stripper to move across the device structure.

The one or more gases may be directed across the surface of thesemiconductor device structure from a central region thereof toward anouter periphery thereof. Alternatively, the one or more gases may bedirected onto a surface of a semiconductor device structure near aperipheral edge thereof so as to move resist stripper across thesemiconductor device structure. Application of one or more gases mayalso be effected in any alternative manner that facilitates thesubstantially continuous movement of resist stripper across the surfaceof the semiconductor device structure.

The one or more gases will preferably not react with (e.g., oxidize orotherwise react with or change the nature of) materials of structures orlayers of the semiconductor device structure that are exposed throughthe photoresist or as the photoresist is removed from the semiconductordevice structure. Gases that may be used in the method of the presentinvention include, without limitation, inert gases or gas mixtures, suchas nitrogen or noble gases (e.g., argon), air, and gaseous hydrochloricacid.

The present invention also includes systems for applying resist stripperto semiconductor device structures in a manner that effects theinventive method. An example of such a system includes a source ofresist stripper, a stripper application component for introducing resiststripper onto a surface of a semiconductor device structure, a gassource, and a gas application component for directing gas at leastpartially across the surface of the semiconductor device structure so asto move resist stripper across the surface. The stripper application andgas application components may be separate from one another or comprisethe same component.

Other features and advantages of the present invention will becomeapparent to those of skill in the art through consideration of theensuing description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic representation of a semiconductor devicestructure including a photomask with resist stripper applied thereto;

FIG. 1B is a schematic representation illustrating another method ofapplying photoresist to a photomask on a semiconductor device structure;

FIGS. 2A and 2B are schematic representations illustrating movement ofresist stripper across the surface of the semiconductor device structureby a gas under pressure;

FIG. 3 is a schematic representation of a variation of the use of a gasunder pressure to move resist stripper across a semiconductor devicestructure when the method of the present invention is used;

FIG. 4 is a schematic representation of the use of gas bubbles in theresist stripper to effect movement of the resist stripper across asemiconductor wafer in accordance with teachings of the presentinvention;

FIG. 5 is a schematic representation illustrating the alternative,nonhorizontal orientation of a semiconductor device structure as amethod according to the present invention is being effected;

FIG. 6 schematically illustrates rotation of a semiconductor devicestructure as a method according to the present invention is beingeffected; and

FIGS. 7A and 7B schematically depict systems for effecting methods thatincorporate teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A schematically illustrates a semiconductor device structure 10,in this case a semiconductor wafer, including a photomask 14 over anactive surface 12 thereof. Photomask 14 is formed from polymerized, orconsolidated, photoresist and may be either soft-baked or hard-baked, asknown in the art. Resist stripper 16 preferably includes ozone (e.g.,ozonated water), but may be any other type of resist stripper known andused in the art. Resist stripper 16 may be applied to photomask 14 byknown processes, such as by spraying resist stripper 16 onto photomask14, as shown in FIG. 1A. As an alternative, resist stripper 16 may beapplied to photomask 14 by at least partially immersing photomask 14 ina quantity of resist stripper 16, as illustrated in FIG. 1B. In anyevent, resist stripper 16 forms a layer 18 over semiconductor devicestructure 10 and over any photomask 14 on active surface 12 ofsemiconductor device structure 10.

In order to effect the method of the present invention, resist stripper16 is exposed to one or more gases 20 or other, nongaseous carrierfluids, which effect movement of resist stripper 16 across semiconductordevice structure 10 or thin layer 18 of resist stripper 16, as shown inFIGS. 2A and 2B. Both of these effects of exposing resist stripper 16 togas 20 facilitate the transfer of reaction products of the reactionbetween resist stripper 16 and the photoresist of photomask 14 away fromthe location where such a reaction is occurring. For example, as resiststripper 16 is moved laterally across semiconductor device structure 10,fresh resist stripper 16 that includes little or no reaction products iscontinuously supplied to locations where resist stripper reacts with thephotoresist of photomask 14. As another example, by thinning layer 18 ofresist stripper 16, reaction products of the reaction between resiststripper 16 and the photoresist of photomask 14 may more readily escapethrough layer 18 than if layer 18 were thicker, thus permitting theaction between resist stripper 16 and the photoresist of photomask 14 tooccur at a faster rate than would be possible if higher concentrationsof these reaction products were present at the locations where thisreaction is occurring. Other methods of exposing resist stripper 16 togas 20 in a manner that may increase the rate at which resist stripper16 removes photoresist of photomask 14 from semiconductor devicestructure 10 are also within the scope of the present invention.

Turning again to FIGS. 2A and 2B, as an example of a way in which resiststripper 16 may be exposed to one or more gases 20, a quantity of gas20, such as nitrogen, air, or gaseous hydrochloric acid, or another,nongaseous carrier fluid, is directed under pressure (either positive(FIG. 2A) or negative (FIG. 2B)) at least partially across layer 18. Gas20 does not include ozone. By directing gas 20 at least partially acrosslayer 18, resist stripper 16 of layer 18 is moved across semiconductordevice structure 10 in a plane substantially parallel to the plane ofsemiconductor device structure 10, such as in the directions of arrows22. In this manner, products of the chemical reaction between the ozoneof resist stripper 16 and the material or materials of photomask 14 arecontinuously moved away from photomask 14, thereby facilitatingsubsequent reactions between the ozone of resist stripper 16 and thephotoresist of photomask 14, as well as the removal of photoresist fromsemiconductor device structure 10, to proceed at a faster rate. Inaddition, by directing one or more gases 20 at least partially acrosslayer 18, the thickness of layer 18 may be reduced, which permitsreactants of the reaction between the ozone of resist stripper 16 andthe photoresist of photomask 14 to more readily pass through layer 18and disperse.

As shown in FIGS. 2A and 3, gas 20 may be directed toward layer 18 in apressurized jet 30. Pressurized jet 30 may be directed toward layer 18from substantially the same location as that from which resist stripper16 is introduced over semiconductor device structure 10, as shown inFIG. 3, or from a different location than that from which resiststripper 16 is directed over semiconductor device structure 10, asdepicted in FIG. 2A.

With reference to FIG. 4, gas 20 may alternatively be directed acrosslayer 18 of resist stripper 16 in the form of bubbles 32 on the surfaceof or residing within layer 18. The movement of bubbles 32 across layer18 may effect the substantially continuous movement of resist stripper16 over semiconductor device structure 10. As bubbles 32 move throughlayer 18, products of the reaction between resist stripper 16 and thephotoresist of photomask 14 may be carried by bubbles 32 away from thelocations in which said photoresist removal reactions are occurring. Inaddition, bubbles 32 may move layer 18 across semiconductor devicestructure 10 as bubbles 32 flow therethrough. Both of these effects ofbubbles 32 facilitate the passage of products of the reaction betweenresist stripper 16 and the photoresist of photomask 14 away from thelocations in which this reaction is occurring, thereby increasing theoverall reaction rate.

FIG. 5 depicts the nonhorizontal orientation of a semiconductor devicestructure 10. When semiconductor device structure 10 is nonhorizontallyoriented, gravity further facilitates thinning of layer 18 and movementof resist stripper 16 in layer 18 over semiconductor device structure10.

Preferably, semiconductor device structure 10 remains substantiallystationary as the method of the present invention is being effected.Thus, existing automated wet bench equipment may be used to conduct themethod of the present invention.

As another alternative, which is illustrated in FIG. 6, a semiconductordevice structure 10 may be rotated in a plane thereof to further effectthinning of layer 18 and movement of resist stripper 16 in layer 18 oversemiconductor device structure 10 by centrifugal force. Again, theadditional thinning and movement of layer 18 provided by such rotationfurther accelerate the rate at which resist stripper 16 removes thematerial or materials of photomask 14 from semiconductor devicestructure 10.

Gas 20 to which layer 18 is exposed may itself increase the rate withwhich resist stripper 16 removes the material or materials of photomask14 from semiconductor device structure 10 or otherwise enhances theremoval of photomask 14 by resist stripper 16. Chemicals or chemicalmixtures that form gas bubbles in layer 18 may also increase the rate atwhich the resist stripper 16 of layer 18 removes the photoresist ofphotomask 14 by action of the bubbles, as discussed previously hereinwith reference to FIG. 4, or by causing the formation of gaseousproducts as resist stripper 16 reacts with the photoresist, whichproducts form and are carried away in bubbles. For example, hydrochloricacid decreases the pH of resist stripper 16 and increases theconcentration of ozone in resist stripper 16, while decreasing theconcentration in resist stripper 16 of carbonic acid (H₂CO₃), which is aproduct of the reaction between an ozonated resist stripper 16 and aphotoresist. In addition, by adding hydrochloric acid to resist stripper16, the concentration of hydrogen ions in resist stripper 16 increases,which forces the carbonic acid in resist stripper 16 to be broken upinto carbon dioxide (CO₂) gas and water (H₂O) rather than into carbonateions (CO₃) and hydrogen ions (H⁺). As a result, more carbon dioxide,which is a gas, is formed. Carbon dioxide readily diffuses, effervesces,or bubbles out of resist stripper 16, away from the reaction betweenresist stripper 16 and the photoresist of photomask 14, and will,therefore, not increase in concentration in the presence of the reactionor decrease the rate at which this reaction occurs. Correspondingly, theformation of carbonic acid, which is an ion that tends to remaindissolved in resist stripper 16, is reduced. Thus, carbonic acidconcentrations will not increase as rapidly as if the hydrogen ions fromhydrochloric acid were not present and, as a result, the rate at whichresist stripper 16 reacts with the photoresist of photomask 14 is notsignificantly decreased. As directing hydrochloric acid toward layer 18of resist stripper 16 increases the formation of carbon dioxide gas inresist stripper 16, the direction of one or more gases 20 toward layer18 may be effected by introducing either gaseous or liquid hydrochloricacid into layer 18. In addition, when hydrochloric acid is used, therate at which resist stripper 16 removes the material or materials ofphotomask 14 may be increased without actually moving layer 18 orthinning layer 18.

FIG. 7A illustrates an exemplary resist stripping system 40 foreffecting the stripping method of the present invention. Resiststripping system 40 includes a wafer support 42, upon which asemiconductor device structure 10 having photoresist thereon ispositioned. Wafer support 42 may be configured to orient a semiconductordevice structure 10 positioned thereon nonhorizontally. Wafer support 42may also be configured to rotate a semiconductor device structure 10positioned thereon. A stripper applicator 44 of resist stripping system40 obtains resist stripper 16 from a source 46 and applies resiststripper 16 to a photomask 14 on a semiconductor device structure 10disposed on wafer support 42. Resist stripping system 40 also includes agas source 48, from which gas 20 is supplied and which communicates witha gas output element 50 that directs gas 20 toward wafer support 42 soas to effect the direction of gas 20 at least partially toward resiststripper 16 or to otherwise expose resist stripper 16 to gas 20.

Alternatively, as shown in FIG. 7B, a resist stripping system 40′incorporating teachings of the present invention may include a chemicaloutput element 54 to which directs a chemical 56, such as hydrochloricacid, from a chemical source 52 toward wafer support 42 so as to exposeresist stripper 16 on a semiconductor device structure 10 positioned onwafer support 42 to chemical 56 and to induce the formation of gasbubbles 32 (FIG. 4) in resist stripper 16.

When methods incorporating teachings of the present invention areemployed, the rates with which these ozonated strippers 16 removehard-baked photoresists are at least about 8,000 angstroms per second upto about 12,000 angstroms per second and greater, as compared withconventional resist stripping methods employing ozonated resiststrippers, which remove hard-baked photoresists at much slower rates.While the methods of the present invention are particularly useful forincreasing the rates with which ozonated resist strippers 16 removephotoresists, the teachings of the present invention may also beemployed to increase the rates with which other types of resiststrippers remove photoresists.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some of the presently preferredembodiments. Similarly, other embodiments of the invention may bedevised which do not depart from the spirit or scope of the presentinvention. Features from different embodiments may be employed incombination. The scope of the invention is, therefore, indicated andlimited only by the appended claims and their legal equivalents, ratherthan by the foregoing description. All additions, deletions andmodifications to the invention as disclosed herein which fall within themeaning and scope of the claims are to be embraced thereby.

What is claimed is:
 1. A method for stripping photoresist from asemiconductor device structure, comprising: exposing the photoresist toa resist stripper; and introducing gas into the resist stripper so as tocause the resist stripper to substantially continuously move relative tothe photoresist.
 2. The method of claim 1, wherein exposing comprisesexposing the photoresist to a resist stripper comprising ozonated water.3. The method of claim 2, wherein introducing gas comprises forming agas other than ozone.
 4. The method of claim 3, wherein introducing gascomprises introducing at least one of an inert gas, a mixture of inertgases, air, and gaseous hydrochloric acid.
 5. The method of claim 1,wherein introducing gas comprises introducing at least one of an inertgas, a mixture of inert gases, and air.
 6. The method of claim 1,wherein introducing gas comprises introducing gaseous hydrochloric acid.7. The method of claim 1, wherein introducing comprises exposing theresist stripper to a chemical that causes the formation of the gas inthe resist stripper.
 8. The method of claim 7, wherein exposing theresist stripper to the chemical comprises exposing the resist stripperto hydrochloric acid.
 9. The method of claim 8, wherein exposing theresist stripper to hydrochloric acid comprises decreasing a pH of theresist stripper so as to cause a carbonic acid product of the strippingto be broken up into water and carbon dioxide.
 10. A method forstripping photoresist from a semiconductor device structure, comprising:exposing the photoresist to a resist stripper; and exposing the resiststripper to a chemical that reacts with at least a component of theresist stripper to form gas therein.
 11. The method of claim 10, whereinexposing comprises exposing the photoresist to a resist strippercomprising ozonated water.
 12. The method of claim 11, wherein exposingresults in forming gas that comprises a gas other than ozone.
 13. Themethod of claim 10, wherein exposing results in the formation of gasthat causes the resist stripper to move substantially continuouslyrelative to the photoresist.
 14. The method of claim 10, whereinexposing comprises exposing the resist stripper to hydrochloric acid.15. The method of claim 14, wherein exposing the resist stripper tohydrochloric acid comprises exposing the resist stripper to gaseoushydrochloric acid.
 16. The method of claim 14, wherein exposing theresist stripper to hydrochloric acid comprises decreasing a pH of theresist stripper so as to cause a carbonic acid product of the strippingto be broken up into water and carbon dioxide.
 17. The method of claim10, further comprising: introducing another gas into the resiststripper.
 18. The method of claim 17, wherein introducing the anothergas comprises introducing at least one of an inert gas, a mixture ofinert gases, and air into the resist stripper.